PROBLEM TO BE SOLVED: To provide a VPN communication system in which stable VPN communication can be performed by transferring a VPN session to another relay server while continuing the VPN communication, in the VPN communication performing communication via a relay server.;SOLUTION: A call control server 202 for establishing a communication session between a plurality of VPN devices 101, 301 performing VPN communication by constructing a VPN on a WAN 200, includes a signal communication part 242 and a relay server selection part 243. The signal communication part 242 receives a relay server change request from a first relay server 203. The relay server selection part 243 then selects a second relay server 204 which is different from the first relay server 203, as a relay server for newly relaying the VPN communication. Then, for the selected second relay server 204 which can relay the VPN communication, the signal communication part 242 transmits to the VPN device 101 a relay server change instruction containing identification information of the second relay server 204.;COPYRIGHT: (C)2011,JPO&INPIT
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